The Development of Crystalline Structure in Aluminium Hydroxide Polymorphs on Ageing

H. Elderfield and J. D. Hem
Department of Earth Sciences, The University of Leeds, Leeds, LS2 9JT
U.S. Geological Survey, Menlo Park, California 94025

Summary: Infrared absorption spectra of the precipitated solids separated from aluminiumhydroxide solutions below the pH of minimum solubility of Al(OH)3 demonstrate the slow ageing of polymeric Al complexes to gibbsite. On comparison with the spectra of natural gibbsites, shifts in absorption frequency during crystal growth are interpreted in terms of changes in hydrogen bonding as a consequence of deprotonation and stacking of aluminium hydroxide layers to form gibbsite. In alkaline solutions the bayerite polymorph precipitates and IR frequencies are compatible with protonation as aluminate ions associate with the bayerite crystal having a lower crystal energy than its low pH polymorph. The infrared spectrum of nordstrandite, which is probably the stable polymorph in alkaline solution, shows evidence of strongly polarized hydroxyl ions similar to gibbsite.

Mineralogical Magazine; March 1973 v. 39; no. 301; p. 89-96; DOI: 10.1180/minmag.1973.039.301.14
© 1973, The Mineralogical Society
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